Fluorescein (abbreviated Fls) is a manufactured organic compound and a dye which is widely used as fluorescent tracer for many applications. Fls exists in several tautomeric forms and in some solid forms.
Among the various crystalline form disclosed in the prior art, particular reference is made to specific solvated and not solvated forms. In particular, Fls Q known as quinoid form (which is a not solvated form, also called red form; also characterized in Angew., Chem. Int Ed Engl., 1997, 36(7), 770-772) has the following formula (I):

Fls Z form, known as zwitterionic form (which is a not solvated form, also called yellow form; see Chem. Eur. J. 2016, 22, 2-20, has the following formula:

Fls L form, known as lactone form, has the following formula:

FlsL, at present, is known only as a solvated form.
WO 2017/082430 discloses a method for the purification of fluorescein sodium by crystallizing fluorescein sodium with 2-propanol or 2-butanol.